Airship launch from a cargo airship

ABSTRACT

A method for launch of an airship includes connecting a cargo airship to a second airship that is not positively buoyant at the launch site, launching the cargo airship, transferring lifting gas from the cargo airship to the second airship where said lifting gas is carried by the cargo airship while aloft; and releasing the second airship from the cargo airship. A high-altitude airship launch system is also provided.

RELATED DOCUMENTS

The present application is a continuation-in-part and claims the benefitunder 35 U.S.C. §120 to U.S. application Ser. No. 13/347,371 filed Jan.10, 2012 to Stephen Heppe, and entitled “Airship Launch from a CargoAirship”, which is a continuation-in-part of U.S. application Ser. No.13/159,215 filed Jun. 13, 2011, now issued as U.S. Pat. No. 8,864,063 onOct. 21, 2014, to Stephen B. Heppe, and entitled “Tethered Airships,”which are incorporated herein by reference in their entirety.

BACKGROUND

High-altitude airships can be used as platforms for a variety ofmissions, including weather and astronomical observations. High-altitudeairships are designed to be lightweight and hold large volumes oflifting gas to provide the desired amount of buoyancy in the upperatmosphere. A stratospheric balloon or airship is generally designedwith a light-weight hull to contain lifting gas while minimizing overallairship mass. For example, airships intended for operation in the upperstratosphere may have a hull with a thickness that is less than 50 μmand an areal density less than 100 g/m² of effective hull surface area,with a surface area on the order of tens of thousands of square meters.

The large surface area and thin hull can make the airship vulnerable todamage, particularly during launch. To launch an airship, a suitablelaunch site is selected and a launch window is selected when little orno wind is anticipated. The launch method restricts the amount of slackballoon material that is subject to wind drag or “sail” effect duringthe launch. The launch site also includes a large open area where theballoon can be laid out and inflated without risk of the fragile hullcoming into undesirable contact with external objects. Here, the bulk ofthe balloon is laid out lengthwise on a suitable launch surface. Verylarge balloons (20-40 million cubic feet displacement; 500,000 to1,000,000 cubic meters displacement) can use 800 ft (240 meters) or moreof layout space. The top portion of the balloon is placed under a rollerarm of a launch vehicle. This launch vehicle confines the lifting gas tothe top portion of the balloon during inflation. At the completion ofinflation, the launch arm is released and the balloon rises verticallyover a payload release vehicle. This payload release vehicle includes acrane that suspends the payload. The payload release vehicle can bedriven downwind to minimize the wind effects on the hull. Even withthese precautions, these launch techniques can only be used in calm ornear calm winds and still result in a significant risk of the hulland/or payloads being damaged. Further, these operational constraintsseverely limit the locations and times that a high-altitude balloon canbe launched.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various examples of the principlesdescribed herein and are a part of the specification. The illustratedexamples are merely examples and do not limit the scope of the claims.

FIGS. 1A and 1B show cargo airships with payload doors that can beopened when launching a high-altitude airship, according to one exampleof principles described herein.

FIG. 1C is a side view of a cargo airship that has been partially cutaway to show storage of a high-altitude airship and launching apparatus,according to one example of principles described herein.

FIG. 1D shows a high-altitude airship being launched from a cargoairship, according to one example of principles described herein.

FIG. 1E is a side view of a high-altitude airship and payload ataltitude, according to one example of principles described herein.

FIGS. 2A and 2B are diagrams showing high-altitude airship with aninflation tube, according to one example of principles described herein.

FIG. 3A-3C show a storage concept for a high-altitude airship carriedwithin a payload bay of a cargo airship, according to one example ofprinciples described herein.

FIG. 4 is a diagram deployment of a high-altitude airship that has beenfolded in a payload bay of a cargo airship, according to one example ofprinciples described herein.

FIG. 5 is a flow chart of a method for deploying a high-altitude airshipfrom a cargo airship, according to one example of principles describedherein.

FIGS. 6A-6B show a flow chart of a method for deploying a high-altitudeairship from a cargo airship, according to one example of principlesdescribed herein.

Throughout the drawings, identical reference numbers designate similar,but not necessarily identical, elements.

DETAILED DESCRIPTION

The figures and specification below describe a two stage deploymentconcept that includes a robust low-altitude airship that can carry ahigh-altitude airship as a payload, and deploy it at a suitablealtitude. The low-altitude airship can be launched (along with itscargo) from a convenient launch site and flown to a different site forthe deployment and launch of the high-altitude airship. This enablesdirect insertion into difficult environments such as polar ormid-oceanic areas.

The robust low-altitude airship can be launched in a greater variety ofwind conditions and a greater variety of launch sites (airports), ascompared to a fragile high-altitude airship, thereby increasing launchopportunities and reducing certain transportation and logistics costs.Also, by deploying the high-altitude airship at a suitable altitude awayfrom the ground while the low-altitude airship (which may also be calledthe cargo airship, first-stage airship, or other suitable name) is indrifting flight, airspeed and wind gusts are minimized, thereby easingthe launch of the high-altitude airship and minimizing the potential fordamage.

The concepts described herein represent a technological alternative tothe special-purpose launch site and special-purpose support equipmentand personnel used for the launch of high-altitude airships.Additionally, the balloon is handled less and risk of damage to the hullis considerably reduced.

Some or all of the expense of building and operating the low-altitudeairship is offset by the avoided expenses associated with somespecial-purpose launch sites and special-purpose support equipment usedfor the launch of high-altitude airships. Also, because of the increasedoperational flexibility of the concepts described herein, costs oflaunching a high-altitude airship can be amortized over a greater numberof launches.

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present systems and methods. It will be apparent,however, to one skilled in the art that the present apparatus, systemsand methods may be practiced without these specific details. Referencein the specification to “an example” or similar language means that aparticular feature, structure, or characteristic described in connectionwith the example is included in at least that one example, but notnecessarily in other examples. In some cases, the components shown inthe figures may not be drawn to scale. Further, the relative scale ofthe components in a given figure may be varied for purposes ofillustration.

FIG. 1A illustrates the general outline of a cargo airship 100 equippedwith a payload bay door or flap 120 on its upper surface. The cargoairship 100 could also be described as a “low-altitude airship”, “firststage airship”, “launch airship”, “logistics tug”, or otherappellations. A payload bay, which is located inside the airship 100,contains a high-altitude airship intended to be launched using theinventive concept. The payload bay communicates with the outsideenvironment via the payload bay door or flap 120. The cargo airship 100comprises sufficient buoyant volume, separated from the payload bay, tocarry itself and its payload to a desired deployment altitude. The cargoairship 100 may be manned, unmanned, or optionally manned. The cargoairship 100 may include other subsystems such as energy or fuel storagesubsystems, propulsion subsystems, aerodynamic control subsystems (suchas lifting surfaces and/or aerodynamic control surfaces), buoyancycontrol subsystems including releasable ballast, and communications,navigation, and control subsystems appropriate to the manning conceptemployed. The payload comprises the high-altitude airship intended to belaunched, support hardware, and optionally, a source of lifting gas forthe high-altitude airship such as e.g. tanks of compressed hydrogen orhelium, or a reservoir of chemical stocks that can be used to generatehydrogen gas at will.

The terms “low-altitude” and “high-altitude”, and their variants, areintended to indicate the relative intended (i.e., “design”) operatingaltitudes of the two airships comprising elements of the inventivesystem. In many examples, the “low-altitude” airship is intended tooperate in the troposphere or lower stratosphere, and the“high-altitude” airship is intended to operate at a substantially higheraltitude than the “low-altitude” airship. In one example, thelow-altitude airship is intended to operate in the lower stratosphere atan altitude of roughly 20 km, and the high-altitude airship is intendedto operate within an altitude range of 25-40 km.

FIG. 1B illustrates the general outline of a cargo airship 110, similarin many respects to the cargo airship 100 previously illustrated,equipped with a payload bay door or flap 130 on its upper and lateralsurface.

FIG. 1C is a side view of a cargo airship 100 that has been partiallycut away to show storage of a high-altitude airship 200 and launchingapparatus (122, 124, 126) in a payload bay. The cargo airship 100includes a number of internal ballonets 128. The ballonets 128 providecontainment of the lifting gas and allow for the distribution of liftinggas to be shifted to achieve more desirable flight characteristics. Inthis example, a space between the ballonets 128 may be used to store:the high-altitude airship 200 on a reel 126; supplies of lifting gas124; as well other gear such as command and control equipment 122. Thepayload bay door 120 is opened to allow the high-altitude airship 200 tobe deployed. As discussed below in greater detail, the hull or ballonetsof the high-altitude airship can be inflated from the supplies oflifting gas 124 and/or from the lifting gas in the ballonets 128 of thecargo airship 100. The reel 126 rotates to allow the high-altitudeairship 200 to be deployed upward through the payload bay door 120 ofthe cargo airship 100 as shown in FIG. 1D. FIG. 1E is a side view of ahigh-altitude airship 200 at altitude with an optional payload 204suspended from the airship by shroud lines 202. In this implementation,the high-altitude airship 200 includes a “pumpkin lobed” hull balloonintended for operation in the upper stratosphere.

FIGS. 2A and 2B illustrate the general outline of one type ofhigh-altitude airship 200 that can be deployed using the inventiveconcepts disclosed herein. As shown in FIGS. 2A and 2B, an inflationtube 210 runs from a point near the crown of the airship to a point nearthe base or collar of the airship. Only a portion of the tube is shownin FIG. 2A.

In FIG. 2B the airship 200 has been illustrated as transparent to showthe full length of the tube 210. The inflation tube 210 allows liftinggas to be selectively introduced into the crown of the airship duringinitial inflation of the airship. By inflating the crown of the airshipfirst, the airship deployment proceeds smoothly and allows the reel tocontinuously unroll the high-altitude airship as the crown of theairship rises out of the payload bay 120, FIG. 1D.

If the high-altitude airship 200 is constructed along the lines of apumpkin-lobed balloon as shown in FIGS. 2A and 2B, the inflation tube210 may be integrated with one of the seams between gores of theballoon. However, other integration methods could be used, includingsupporting the inflation tube 210 from the crown of the airship so thatthe tube hangs down the center of the airship when the airship 200 isinflated. The purpose of the inflation tube 210 is to allow hydrogen gasto be introduced in such a way that the crown of the airship is thefirst portion to be significantly inflated, as opposed to its base (moregenerally, the purpose of the inflation tube is to first inflate thepart of the high-altitude airship or balloon that is outermost on thedrum or spindle 250, and which will be deployed first).

FIG. 3A illustrates a general stowage concept for a high-altitudeairship carried within the payload bay of the cargo airship 100 (or110), in accordance with one example of the present specification. Thisparticular example is adapted to the form of the airship 200 illustratedin FIG. 1A-1D, but may be used for certain other airship types andgeometries as well. As illustrated in FIG. 3A, the hull comprising theenvelope of the lifting volume of the high-altitude balloon or airship200 is wound loosely on a reel 255. In this example, the reel 255includes a spindle 250 between end plates 260 and 270. The reel 255 maybe supported by additional equipment that is not shown and may include avariety of additional components including motors, brakes, and sensors.

The inflation tube 210 is constructed to resist crushing so that itmaintains an open cross-section along its entire length when subjectedto the expected compression loads associated with the hull of thehigh-altitude airship 200 (along with the inflation tube 210 itself)being wound on the reel 255. As the airship 200 is wound onto the reel255, tension in the direction of winding is carefully managed to insurethat compressive forces do not crush the inflation tube 210.

The inflation tube 210 is connected, through the action of a commandablevalve that is part of the balloon 200, and a reversible matingapparatus, to a filling port on the reel 255. The filling port, in turn,is fluidically connected to an external supply of lifting gas. One ormore of these connections includes a rotating joint (such as a slip ringjoint) that allows a first half of the connector to rotate with the reel255. The other portion of the connector is connected to the external gassupply and remains stationary.

The inflation tube 210 may include one or more diffusers on its terminalend to ensure that hydrogen gas is distributed into the crown of theballoon without damage to the balloon material by the temperature orpressure of the hydrogen. For example, if the hydrogen is taken fromcryogenic storage, the hydrogen may be very cold. The diffuser allowsthe hydrogen to be more effectively distributed and warmed. The diffusermay include an end cap with multiple openings, multiple openings alongthe length of the tube, or other appropriate configuration. The diffusermay allow the hydrogen to be delivered at higher pressures for morerapid inflation of the balloon. Further, if the tube is used to extractgas from the balloon, the diffuser provides multiple openings that areless likely to be blocked.

In operation, the apparatus and structures illustrated generally in FIG.3A allows the high-altitude airship 200 to be filled with lifting gaseven while it is being unspooled from the drum or spindle 250.Specifically, after the cargo airship 100 (or 110) reaches a desireddeployment and launch altitude, and is allowed to drift with the wind sothat it achieves close to zero airspeed, the payload bay door or flap120 is opened or retracted, exposing the payload bay with itshigh-altitude airship 200 wound on the reel 255. A small amount oflifting gas is introduced into the high-altitude airship 200 by way ofthe previously-noted plumbing contained in the drum or spindle 250, thefilling port, the reversible mating apparatus, the commandable valve,and the inflation tube 210. This causes the crown of the high-altitudeairship (or other portion that is wound outermost on the drum or spindle250) to inflate, become buoyant, and start to pull upward and away fromthe reel 255. This will naturally tend to cause the drum or spindle 250to unwind. Additional lifting gas can be introduced as alreadydescribed, taking care to avoid an excessive inflation rate that couldcause the hull of the high-altitude airship to rupture. A motor andbrake apparatus, associated with the reel 255 is included in someexamples to enhance the deployment sequence by assisting in initialdeployment (through motorized turning of the drum or spindle) and alsoslowing the rate of deployment (braking, if necessary).

As illustrated in FIG. 3A, even in its “stowed” or “wound”configuration, a small portion of the high-altitude airship may remainsubstantially “unwound” on the drum or spindle 250, so as to facilitateinitial inflation and the creation of a suitable “bubble of gas” thatwill achieve positive buoyancy (so that it floats upward and away fromthe drum or spindle 250).

In another example, an inflation tube or functionally similar structureis connected to a portion of the high-altitude airship that isaccessible or “exposed” on the outer layer of the high-altitude airshipas it is wound on the drum or spindle 250. In another example, theinflation tube is connected to a portion of the high-altitude airshipthat is initially not wound on the drum or spindle, and this portion ofthe high-altitude airship is also releasably secured to a fixture orstay on the cargo airship. For example, an equipment package of thehigh-altitude airship including a “fill port” with a commandable valveis releasably secured on the outer surface of the cargo airship, whilethe majority of the hull of the upper airship is spooled on a drum orspindle inside a cargo bay of the cargo airship or alternatively foldedin a configuration to facilitate proper deployment. Upon initialinflation with lifting gas via the fill port, a “bubble” of lifting gaswill form inside a portion of the hull of the high-altitude airship thatis in close proximity to the fill port, and will serve to extract theremainder of the high-altitude airship from the cargo bay. Followingproper inflation, the commandable valve is commanded to a closedposition, the connection to the inflation tube is severed, and thehigh-altitude airship is released. In this example, a rotating joint isnot used thereby avoiding the need to ensure that the filling tuberemains “open” along its length while it is wound on the reel andspindle.

In yet another example, a long tube is connected to a fill port with acommandable valve located on an externally-accessible portion of thehigh-altitude airship, and this portion is allowed to lift away from thecargo airship during the inflation process. This example uses a longerfilling tube, but avoids the need for a separate releasable structuresecuring the equipment package and fill port to the cargo airship.

As the high-altitude airship 200 is unwound from the drum or spindle250, and inflated with lifting gas, the combined system of the cargoairship 100 (or 110) and high-altitude airship 200 becomes more buoyant(i.e., since the total mass is the same but the total lifting volumefilled with lifting gas is increased), and so it tends to seek a higheraltitude. The local wind field may change for this and other reasons,but the combined system tends to drift with the lateral wind (althoughthere is a lag in responding to changes in the wind field) and airspeedtends to remain low. This has the effect of protecting the high-altitudeairship 200 from damage due to high winds during deployment. Whenapplicable, the cargo airship 100 (or 110) can be operated (maneuvered)to actively follow the winds, using its maneuvering and propulsioncapability to overcome its own inertia and thereby help to minimize thelocal airspeed experienced by the high-altitude airship 200 during itsdeployment. Furthermore, in some examples, the cargo airship 100 (or110) can actively control its own buoyancy, for example by droppingballast, venting lifting gas or pumping lifting gas into a reservoir(thereby allowing its lifting volume to be reduced). Alternatively,propulsive forces (such as propellers or fans adapted to provide adownward force) can be utilized to counteract the increase in buoyancy.In such examples, the altitude of the combined system can be heldrelatively constant during the deployment sequence.

The amount of lifting gas introduced into the high-altitude airship canbe metered to ensure that a proper amount of lifting gas is introducedto take the airship to its desired altitude, while guarding against overinflation. When the proper amount of lifting gas has been introduced,and the high-altitude airship is fully unspooled from the drum orspindle 250, the commandable valve is closed and the reversible matingapparatus is operated to demate the airship 200 from the mating fixtureof the drum or spindle 250. The high-altitude airship then ascends fromthe cargo airship 100 (or 110), while the cargo airship 100 (or 110)itself descends to a lower altitude.

If the high-altitude airship 200 is associated with a payload, perhapsconnected to the airship with shrouds so that the payload will besuspended below the airship during operation, the apparatus of FIG. 3Acan be modified or adapted as illustrated in FIGS. 3B and 3C. Here, endplate 270 has been removed from the illustration for clarity (althoughit is present in the intended apparatus) and drum or spindle 250 hasbeen replaced with fixed cylindrical segments 252 and 257 and movablecylindrical segments 254 and 259. The movable segments 254 and 259 areconnected to the fixed segments 252 and 257 through hinge lines 253 and258, and can open outward under the influence of remotely commandablelatches, springs, or other actuators. The payload 204 is secured to thefixed cylindrical segments 252 and 257, and held within the generallycylindrical space as illustrated, by remotely commandable, reversiblylatchable mounting apparatus not explicitly shown. Shroud lines 202 areillustrated schematically as extending from the payload 204 and wrappingaround the fixed and movable cylindrical segments already described.Numerous turns of the shroud lines 202 on the cylindrical segments couldexist, followed by the high-altitude airship itself. As notedpreviously, the high-altitude airship 200 comprises an inflation tube210, commandable valve, and reversible mating apparatus which in thisexample is connected to a filling port 280 located axially on the endplate 260. A variety of additional components may also be included. Forexample, a short tube may be used to span the distance from the airshiphull itself, which may be outside the generally cylindrical spacebounded by the cylindrical segments 252, 254, 257 and 259, and thereversible mating apparatus connected to the filling port 280.

In operation, the high-altitude airship 200 is unwound from theapparatus illustrated in FIGS. 3A-C. However, the unwinding activity ispaused when the high-altitude airship 200 is clear of the apparatus. Thecommandable valve is then closed. In one example, a hull integrity checkcan be performed at this stage and, if a breach in the hull is detected,the high-altitude airship can be vented of its lifting gas and rewoundon the illustrated apparatus, and returned to the ground for repair(alternatively, if it is infeasible to re-stow the airship, it can bejettisoned and only the payload can be returned to the ground). If nofault is detected, the reversible mating apparatus is operated to dematefrom the filling port 280. The unwinding activity is then continued,until the shroud lines are fully extended. At this stage, the rotationof the apparatus is again halted. The movable segments 254 and 259 arecommanded open and pivot on hinge lines 253 and 258, respectively, asshown in FIG. 3C. The remotely commandable latches holding the payload204 in place are then commanded open, releasing the payload 204 and theentire high-altitude airship 200 from the cargo airship 100 (or 110).

OTHER EXAMPLES

In another example, instead of a rotatable reel, the high-altitudeairship is folded and stowed in an accordion fashion within the payloadbay of the cargo airship. FIG. 4 illustrates a partially-filledhigh-altitude airship at an early point in the deployment processassociated with such an example. The high-altitude airship 200 is shownpartially folded and partially inflated. The figure illustrates areservoir of lifting gas 420, a remotely operable valve 422, and a gasline 425 fluidically connecting the valve 422 to a remotely operablemating apparatus 430 which is mated to a gas fill port on the collar 440of the high-altitude airship 200. The collar 440, in turn, comprises asecond remotely operable valve (not shown) connecting the gas fill portto the inflation tube 210, which was previously discussed. Also shown isa bracket 450 and remotely operable latch 475 which holds the collar ofthe high-altitude airship in place until the latch 475 is released. Thepayload 204 is attached to the collar 440 by shroud lines 202. Inoperation, the remotely operable valves are operated to fill the airshipwith a suitable amount of lifting gas from the reservoir 420. Thehigh-altitude airship inflates and extracts (or substantially extracts)itself from the cargo bay. The remotely operable valves are closed and,in one example, a hull integrity check is performed. The remotelyoperable mating apparatus 430 is operated to demate from the collar ofthe high-altitude airship, and the remotely operable latch 475 isoperated to release the high-altitude airship 200 along with its payload204.

In another example, the high-altitude airship is secured to the top ofthe cargo airship rather than being stowed internally within a payloadbay. In this example, if the high-altitude airship is associated with apayload, the payload may be stored in a payload bay, or it also may besecured externally to the cargo airship, and released when required.

Deployment of a Tethered Airship System

In the implementation described below, the numerical examples areapproximate and intended to illustrate general principles of theinventive concept as opposed to a precise design. Further, a number ofsimplifying assumptions, such as ignoring temperature differences, areused in the illustrative calculations.

Consider a tethered airship system in accordance with U.S. applicationSer. No. 13/159,215 comprising a lower airship, an upper airship and atether connecting the two airships. In one example described the presentspecification, the upper airship and tether is initially launched fromthe ground, and carried as a payload of the lower airship. As oneexample of the principles described herein, assume that the lowerairship weighs ˜5000 kg, is designed to operate in a altitude range of18 to 19 km, and comprises a maximum lifting volume of 44,700 m³ in oneor several ballonets that can withstand a maximum pressure difference of2 kPa (i.e., they can be deflated, or partially inflated, or fullyinflated to ambient pressure, or fully inflated to a pressure up to 2kPa above ambient pressure). Assume the upper airship weighs ˜2150 kg,is designed to operate in an altitude range of 27 to 37 km, andcomprises a maximum lifting volume of 500,000 m³ in a balloon that canbe inflated to a maximum pressure difference of 100 Pa relative toambient pressure. Assume that the tether weighs 600 kg.

Initially, the total weight of all systems is 7750 kg and the lowerairship, considering its maximum lifting volume, can carry this totalweight to an altitude in excess of 15 km. At this altitude, atmosphericdensity is about 0.193 kg/m³ and the density of an equivalent volume ofhydrogen is about 0.0015 kg/m³. If this is rounded up to 0.002 kg/m³,the reader will appreciate that the lifting capacity of the lowerairship will be about 0.191 kg/m³ and only 44,000 m³ of lifting volumewould be sufficient to carry 8400 kg (650 kg more than the total systemweight) to 15 km. Hence the lower airship can carry the total system to15 km with some design margin (i.e., the ballonets do not require fullinflation at 15 km altitude in order to carry the total system weight).

With the system as described, the total system is in buoyant equilibriumat about 15 km altitude with most or all of the lifting volume of thelower airship operated at ambient pressure (i.e., some or all of theballonets may be partially inflated, and pressurized sections of thehull intended to maintain a rigid aerodynamic shape have been ignoredfor this calculation). The lifting gas, which is at ambient pressure,could be transferred from one ballonet to another within the lowerairship without affecting total system buoyancy. Similarly, some of thelifting gas could be transferred at atmospheric pressure from theballonets of the lower airship, to the upper airship, without affectingtotal system buoyancy. Hence, the upper airship could be filled with asufficient quantity of lifting gas to carry the upper airship and thefull weight of the tether to the maximum design altitude of 37 km, wherethe upper airship would be fully inflated and would experience atinternal pressure roughly 100 Pa above ambient. However, prior torelease, the upper airship and lower airship are both at thepre-existing equilibrium altitude since the total lifting volume has notchanged (it has only been shifted from one part of the system toanother). The volume of gas, at ambient pressure at 15 km, required tocarry the upper airship plus tether to that altitude is roughly

(2150+600)/0.191≈14,400 m³,

or roughly one-third of the original lifting volume of the lowerairship. If carried to an altitude of 37 km, and allowed to expand tomatch atmospheric pressure at that altitude (420 Pa), this volume oflifting gas would expand to roughly 415,000 m³. If instead, a volume ofapproximately 21,600 m³ of lifting gas is transferred (at 15 km wherepressure is nominally 12,045 Pa), the upper airship could be operated at37 km at its full volume of 500,000 m³ and full internal pressure of 520Pa (i.e., 100 Pa above ambient).

After a transfer of 21,600 m³, the lower airship has an effectivelifting volume of roughly 22,400 m³ or less, considering that it startedwith less than 44,000 m³. Hence, its lifting capacity is no more than(22,400 m³)*(0.191 kg/m³)≈4300 kg. This is less than the weight of thelower airship (5000 kg). If the upper airship is released and allowed toascend to 37 km altitude, it will provide a buoyancy force of (500,000m³)*(0.0055 kg/m³)=2750 kg; roughly the weight of the upper airship plusthe tether. So the total lifting force is no greater than 6950 kg, whichis less than the total system weight (7800 kg). Hence, the lower airshipwill not be able to maintain its altitude as the upper airshipascends—additional lifting gas is be added to the lower airship in orderto increase buoyancy, and actually achieve the intended operationalaltitude of about 18 km. In order for the lower airship to carry its ownweight ignoring the tether, at an altitude of 18 km where atmosphericdensity is 0.1207 kg/m³ and atmospheric pressure is 7,505 Pa, and thelifting capacity of hydrogen is roughly (13/14)*0.1207˜0.112 kg/m³, thelower airship is to attain a lifting volume of roughly 44,600 m³. Thissame amount of lifting gas, at the initial deployment altitude of 15 kmwhere atmospheric pressure=12045 Pa, comprises a volume of roughly(44,600 m³)*7505/12045˜27,800 m³. Hence, adding to the remainingcomplement of the lower airship (roughly 22,400 m³ of lifting gas afterthe inflation of the upper airship), roughly 5400 m³ of hydrogen gas isto be added at the ambient atmospheric pressure of 12045 Pa. This can beadded from an internal reservoir carried by the lower airship(cryogenic, non-cryogenic, or chemical), or an external tanker/logisticsairship adapted to provide additional lifting gas.

In the example just described, some of the need for additional liftinggas could be alleviated by utilizing the full lifting volume of thelower airship. It may also be feasible, for some examples, to tailor theinitial operation of the lower airship so that it experiences a positivepressure differential (inside pressure compared to outside) atequilibrium altitude prior to the transfer of lifting gas to the upperairship. This would leave the lower airship with a slightly greatervolume of lifting gas following the transfer of gas to the upperairship, thereby minimizing the need for replenishment gas from aninternal reservoir or external tanker/logistics airship. However, caremust be taken when performing such an operation since the tendency, uponinitiating the transfer of gas, will be for the total system to riseslightly in altitude (i.e., since the lifting volume of the upperairship increases, but the lifting volume of the lower airship remainsunchanged since its lifting volume is initially pressurized relative toambient pressure). Thus, care must be taken to ensure that the designparameters of the lower airship (specifically, maximum pressuredifferential) are not exceeded in any of its ballonets or its liftingvolume as a whole.

In one example, the lower airship is augmented with a cryogenicreservoir of lifting gas (which increases its weight), loaded with theupper airship and its associated deployment apparatus, and inflated toachieve neutral buoyancy at full ballonet inflation, but withoutoverpressure, at an altitude below its intended operating altitude.Following the transfer of lifting gas to the upper airship, anddeployment of the upper airship to a higher altitude, the lower airshipreplenishes its lifting volume with lifting gas from the cryogenicreservoir. The cryogenic reservoir may be retained on the lower airshipfor the life of the mission, or it may be jettisoned in a safe areawhere it will not pose a risk to life or property on the ground (e.g.,an oceanic area). In an example where the cryogenic reservoir isjettisoned, the weight of the empty reservoir represents ballast whichwould tend to reduce the equilibrium altitude of the lower airship priorto being jettisoned (and specifically, during the transfer of liftinggas from the lower airship to the upper airship). At the lowerequilibrium altitude, the ballonets at full inflation hold a largerquantity of lifting gas (i.e., a larger mass of lifting gas) than theywould at a higher equilibrium altitude. Thus, after transferring adesired quantity of lifting gas to the upper airship, a greater amountof lifting gas remains in the lower airship, thereby reducing the sizeof the cryogenic reservoir needed to “top off” the lifting volume of thelower airship.

If a reservoir of lifting gas is available during gas transfer to, andinflation of, the upper airship, or equivalently if a tanker/logisticsairship is available during this process, there could also be a transferdirectly from the reservoir (or tanker/logistics airship) to the upperairship, for at least some of the required lifting gas, thereby avoidingthe need to deplete and subsequently replenish the lower airship.

In another example, the transfer of lifting gas from the lower (cargo)airship to the upper airship is performed at an altitude where the totalamount of lifting gas, used by both airships at their ultimateoperational altitudes, can be accommodated within the lifting volume ofthe lower airship. For example, consider a tethered airship system asbefore where the lower airship weighs 5000 kg and is designed foroperation at 18 km with a total lifting volume of 44,700 m³, the upperairship weighs 2150 kg and is designed for operation up to 37 km with atotal lifting volume of 500,000 m³, and the tether weighs 700 kg. If thetransfer is performed at an altitude of 10 km, ambient atmosphericpressure is approximately 26.5 kPa and the internal pressure of thelower airship can be maintained at 27.5 kPa using internal ballonetsfilled with atmospheric gases to an overpressure (relative to ambient)of 1 kPa. Under these conditions, all the lifting gas for both airshipsis compressed into a volume of approximately 25,000 m³. This issubstantially less than the total lifting volume of the lower airshipwhich, as noted above, is 44,700 m³. So no extra storage facilities,cryogenic or otherwise, are needed. However, the lifting capacity ofhydrogen gas at this altitude, held at 1 kPa overpressure, is roughly383 g/m³. So the total lifting capacity is roughly (25,000 m³)·(0.383kg/m³)≈9550 kg which exceeds the total system weight by roughly 1700 kg.So the system is positively buoyant at 10 km altitude and will tend torise, requiring the transfer to be completed quickly in order to avoidrisk of rupturing the lifting ballonets of the lower airship. This riskcan be mitigated by adding an additional releasable mass or ballast tothe lower airship, where it is understood that the releasable mass has adensity greater than air. For example, if 1850 kg of water ballast isinitially carried aloft, the combined system will be neutrally buoyantat less than 10 km altitude prior to the transfer, and will be neutrallybuoyant at roughly 10 km altitude after the transfer (i.e., consideringthe lower density of lifting gas in the upper airship versus the lowerairship), and the transfer of lifting gas can be performed in aleisurely manner without undue risk. The water ballast can be releasedafter the transfer is complete, in order to allow the tethered airshipsystem to achieve its intended operational altitudes (i.e., in thisexample, 18 km for the lower airship, and up to 37 km for the upperairship). If excess water ballast is initially carried aloft, it can be“metered out” in a controllable release in order to achieve a desiredequilibrium altitude for the transfer.

In one example, in lieu of some or all of the water ballast, the lowerairship further comprises a detachable (releasable) unmanned air vehiclecontaining a pump which is adapted and plumbed to facilitate thetransfer of lifting gases from the lower airship to the upper airship.The unmanned aerial vehicle represents a releasable mass which iscarried aloft by the lower airship. Following the transfer, theconnections to the lower airship are severed (with commandable valveshaving been commanded closed to avoid the unintended release of liftinggas), the unmanned air vehicle is released, and it is flown back to aselected landing or recovery site for a safe recovery. This example isparticularly desirable when a pump is used to facilitate the transfer oflifting gas, but is not used subsequent to the transfer, and wouldtherefore represent “dead weight” carried by the lower airship duringits operational mission.

In order to avoid the need for ballast tanks and valves on the lowerairship, which would also represent “dead weight” during the operationalmission, the unmanned air vehicle can carry all the extra ballast neededby the system. The unmanned air vehicle can drop the ballast before itis itself released from the lower airship, or after said release.

The unmanned air vehicle can perform other desirable functions, such asproviding for auxiliary thrust and/or aerodynamic control during initialtakeoff and low-altitude operations of the low altitude/cargo airship.

In another example, the low-altitude/cargo airship comprises a cargo baythat extends vertically through the entire airship, with doors, hatches,or openings on the upper surface and lower surface of the hull. Theupper airship's deployment mechanisms, a pump to facilitate the transferof lifting gases, and additional ballast as needed, are assembled into adetachable subsystem that can be released and jettisoned through thelower door, hatch or opening. The detachable subsystem comprises areleasable mass. Following the successful deployment of the upperairship, and after closing valves to prevent the undesired release oflifting gas, the detachable subsystem is released and jettisoned. It canbe allowed to fall into the ocean or an uninhabited area with or withouta parachute, or it can be adapted to deploy wings and fly back to adesired recovery site.

The upper airship of a tethered airship system may comprise multipleelements such as a buoyant element (such as a high-altitude balloon) atthe high end of a tether, a parafoil, a parachute, and a docking elementfor a shuttle designed to move up and down the tether, with theparafoil, parachute, and docking element attached (and controlled from,as applicable) subsystems spaced apart along the tether. The tetheredairship system may also comprise elements such as the aforementionedshuttle that moves up and down the tether, and elements associated withthe lower airship such as tether attachment/deployment mechanisms andsheaths designed to protect other elements of the system from abrasionand wear. In some examples, all of these elements may be “stacked” inaccordion fashion prior to deployment, in a generalization of thestowage concept illustrated in FIG. 4. In other examples, the upperairship, its associated parafoil, parachute, docking elements (and theirattachment and control apparatus) and a portion of the tether are stowedon a rotatable spool as indicated generally in FIG. 3. As part of thedeployment sequence, the lower end of the tether deployed from saidrotatable spool is transferred and attached to the end of anothersegment of tether which is associated with the rest of the system. Instill other examples, the rotatable spool used for stowing and deployingthe upper airship and its associated elements is integrated with the“high-altitude” docking element for the shuttle (this docking elementbeing the lower-most mechanical element associated with the upperairship). The docking element is in turn attached to the end of anothersegment of tether which is associated with the rest of the system. Allattachments are made on the ground and verified prior to launch. Thisexample avoids the engineering challenge and mission risk of making andensuring a secure attachment between two elements during the deploymentsequence.

The specific details described above are merely examples. The principlesdescribed herein are not limited to the examples disclosed. Theprinciples could be used with a wide range of airships and in a widevariety of configurations. In general, a method for launch of an airshipcomprises connecting a cargo airship to a deflated (or partiallyinflated) second airship that is not positively buoyant at the launchsite, and launching the cargo airship. The cargo airship carries thesecond airship aloft and inflates the second airship with lifting gascarried by the cargo airship. The second airship is then released fromthe cargo airship. FIGS. 5 and 6 are flowcharts that describe methodsfor launching airships from a cargo airship.

FIG. 5 is a flow chart describing a method 500 for deploying ahigh-altitude airship from a cargo airship. The upper airship is stowedin the cargo airship (block 505). The cargo airship is launched andtravels to a designated location (block 510). Deployment of the upperairship begins by opening the payload bay and opening a valve to allowlifting gas to flow through an inflation tube into the crown of theupper airship (block 515). The crown of the upper airship inflates andprogressively lifts out of the payload bay as more lifting gas passesthrough the inflation tube (block 520). The upper airship receives thedesired amount of lifting gas, lifts its payload from the payload bay ofthe cargo airship, and ascends to the desired altitude (block 525).

The method described above is merely one example and could be altered ina variety of ways. The blocks could be deleted, added, combined orreordered. For example, additional blocks could be added to describeshutting the valve after the desired amount of lifting gas has beenreceived by the high-altitude airship or opening a reel to release thepayload from the payload bay.

FIGS. 6A and 6B show a more detailed method 600 for deploying ahigh-altitude airship from a cargo airship. In this example, thehigh-altitude airship and its payload (if any) are stowed in a payloadbay of the cargo airship (block 605). As discussed above, the hull ofthe high-altitude airship may be stowed in a variety of configurations,including wrapped around a reel or a number of folded configurations.The payload and other items, such as parachutes, tethers, parafoils, andother items, can be appropriately attached to the hull and stowed fordeployment out of the payload door in an upper surface of the cargoship. The high-altitude airship includes a tube that passes from asource of lifting gas through the length of the uninflated hull to thecrown of the hull.

The cargo airship is launched and travels to a predetermined altitudeand location (block 610). In some examples, the cargo airship may use acombination of buoyant lift, vectored thrust, ballast, aerodynamic lift,and pressure control of ballonets to maintain the desired heading,altitude, and velocity. For example, if the total mass of the cargoairship and its payload exceeds the buoyant lifting capacity of thecargo airship, the cargo airship could use vectored thrust andaerodynamic lift to increase its lifting capacity. The vectored thrustcould be generated in a variety ways, including the use of directionalducted fans. Aerodynamic lift can be created through the geometry and/orangle of attack of the airship and lifting surfaces attached to theairship.

The cargo ship then transitions into drifting flight while launching thehigh-altitude airship (block 615). Drifting flight can include a varietyof maneuvers and propulsion schemes that minimize the speed of winds onthe upper airship below a predetermined threshold as it is beinginflated and launched. For example, drifting flight may includecontrolling the cargo ship so that it travels approximately the samespeed and direction as the surrounding air. Drifting flight may alsoinclude using propulsion to alter the speed or orientation of the cargoairship to maintain the desired heading. In some circumstances, driftingflight may include slight differences between the speed of the cargoairship and the surrounding air. These slight differences may be used toapply desirable aerodynamic forces on high-altitude airships.

The launch of the high-altitude airship includes opening a payload doorin the upper surface of the cargo airship and opening a commandablevalve to allow lifting gas to flow through the inflation tube into thecrown of the high-altitude airship hull (block 620). It may also involvethe use of a pump to facilitate the transfer of lifting gas. As the hullinflates the high-altitude airship is progressively deployed out of thepayload bay (block 625). When the desired amount of lifting gas has beentransferred from a lifting gas reservoir to the upper airship, thecommandable valve is closed (block 630).

Continuing in FIG. 6B, a hull integrity check is performed (block 635).The hull integrity check may include a variety of sensors and techniquesdesigned to determine if a hole or a rip in the hull is allowing liftinggas to escape. The hull integrity check may include sensing pressurechanges in the hull, imaging the interior or exterior of the hull,detecting a change in the lifting capacity of the high-altitude airship,or other appropriate technique.

An evaluation of the hull integrity is then made (block 640). If theevaluation indicates that the hull integrity is not satisfactory, thehigh-altitude airship can be jettisoned or the lifting gas can beremoved and the high-altitude airship restowed in the payload bay (block645). Jettisoning the high-altitude airship may include actions such asfiring a pyrotechnic cutter to cut the shroud lines that attach the hullof the airship to the payload. The hull and the lifting gas remaininginside the hull then rise rapidly away from the cargo airship. Restowingthe high-altitude airship allows the airship to be returned to theground for repair or replacement. The lifting gas can be removed using avariety of techniques, including venting the lifting gas and/or pumpingthe lifting gas out of the hull. Lifting gas that is pumped out of thehull can be stored in pressure tanks or returned to ballonets in thecargo ship. After the damaged hull of the upper airship has beenjettisoned or restowed, the cargo airship can return to the ground forreplacement or repair of the high-altitude airship (block 650).

If the hull integrity is determined to be satisfactory (“Yes”) thepayload can be released from the cargo airship to allow the upperairship to ascend (block 655). The high-altitude airship may be freeflying or may be connected to the cargo airship by a tether. Afterdeployment of the high-altitude airship, there may be one or morelifting gas reservoirs that are empty. These depleted lifting gasreservoirs can be jettisoned to improve the endurance and buoyancy ofthe cargo airship (block 660).

In sum, a two stage deployment concept that includes a robust cargoairship that can carry a high-altitude airship as a payload, travel to adesired deployment location and deploy the high-altitude airship at asuitable altitude. This enables direct insertion into difficultenvironments such as polar or mid-oceanic areas. By deploying the upperairship while the cargo airship is in drifting flight, winds can beminimized. This allows for easier launch and lower damage risk to theupper airship. The cargo airship can be launched in a wide variety ofwind conditions and sites. This greatly increases the available launchwindows for upper airships.

The preceding description has been presented merely to illustrate anddescribe examples of the principles described. In some of the figuresthe relative dimensions of components have been altered for purposes ofdescription. This description is not intended to be exhaustive or tolimit these principles to any precise form disclosed. Many modificationsand variations are possible in light of the above teaching.

What is claimed is:
 1. A method for launch of an airship comprising:connecting a cargo airship to a second airship which is not positivelybuoyant at the launch site, the cargo airship comprising propulsive andmaneuvering capabilities; launching the cargo airship, the cargo airshipcarrying the second airship aloft and traveling to a predeterminedlocation using the propulsive and maneuvering capabilities of the cargoairship; while aloft, transferring lifting gas from the lifting volumeof the cargo airship to the lifting volume of the second airship; andreleasing the second airship from the cargo airship.
 2. The method ofclaim 1, in which the second airship has a maximum operational altitudethat is at least 5 km higher than the maximum operational altitude ofthe cargo airship.
 3. The method of claim 1, in which the second airshiphas a maximum operational altitude in excess of 25 km, and the cargoairship has a maximum operational altitude in excess of 20 km, and themaximum operational altitude of the high-altitude airship is at least 5km higher than the maximum operational altitude of the cargo airship. 4.The method of claim 1, further comprising placing the cargo airship indrifting flight during inflation of the second airship.
 5. The method ofclaim 1, in which the transfer of lifting gas is performed at analtitude where the total amount of lifting gas needed for the cargoairship to achieve its operational altitude, and for the second airshipto achieve its operational altitude, can be accommodated within thelifting volume of the cargo airship.
 6. The method of claim 5, furthercomprising the release of a releasable mass from the cargo airshipfollowing the transfer of lifting gas.
 7. The method of claim 6, inwhich the releasable mass is an unmanned aerial vehicle.
 8. The methodof claim 1, in which: connecting a cargo airship to a second airshipcomprises stowing a high-altitude airship in a payload bay of the cargoairship; transferring lifting gas comprises opening a commandable valveto allow lifting gas to flow through an inflation tube into thehigh-altitude airship such that the high-altitude airship inflates andprogressively lifts the high-altitude airship out of a payload bay; andreleasing the high altitude airship comprises releasing a payloadconnected to the high-altitude airship from the cargo airship, thehigh-altitude airship lifting the payload from the payload bay.
 9. Themethod of claim 8, in which stowing the high-altitude airship in thecargo airship comprises wrapping the high-altitude airship around a reelin the payload bay.
 10. The method of claim 9, further comprisingloading the payload of the high-altitude airship into the center of thereel and opening the reel to release the payload.
 11. The method ofclaim 8, in which stowing the high-altitude airship in the payload bayof the cargo airship comprises folding the high-altitude airship in thepayload bay.
 12. The method of claim 8, further comprising opening apayload bay door prior to inflation of the high-altitude airship.
 13. Ahigh-altitude airship launch system comprising: a high-altitude airshipcomprising: a hull; and an inflation tube comprising a first endconnected to a gas source and a second end terminating in thehigh-altitude airship; and a cargo airship comprising: propulsive andmaneuvering capabilities; a lifting gas reservoir; a releasable mass;and a commandable valve; in which the cargo airship transports thehigh-altitude airship aloft and travel to a predetermined location usingthe propulsive and maneuvering capabilities and inflate thehigh-altitude airship while in controlled flight by opening thecommandable valve and passing lifting gas from the lifting gas reservoirthrough the inflation tube into the high-altitude airship.
 14. Thesystem of claim 13, in which the inflation tube is disposed inside thehull of the high-altitude airship.
 15. The system of claim 13, in whichthe second end of the inflation tube terminates near a crown of thehull.
 16. The system of claim 13, in which the inflation tube passesthrough a gore in the hull of the high-altitude airship.
 17. The systemof claim 13, in which the cargo airship further comprises an internalpayload bay to receive the high-altitude airship.
 18. The system ofclaim 17, in which the cargo airship further comprises a retractablepayload door on an upper surface of the cargo airship.
 19. The system ofclaim 13, in which the cargo airship further comprises a reel disposedin the payload bay, the high-altitude airship being wrapped around thereel such that the crown is exposed and the inflation tube maintains anopen cross section along the length of the inflation tube.
 20. Thesystem of claim 19, in which a payload of the high-altitude airship iscontained with the reel, the reel comprising movable segments to open torelease the payload.
 21. The system of claim 13, in which the inflationtube further comprises a diffuser at the second end.
 22. The system ofclaim 13, further comprising a tether connecting the high-altitudeairship and the cargo airship, the tether having a length sufficient toallow a separation of at least 10 kilometers between the high-altitudeairship and the cargo airship.
 23. The system of claim 22, in which atleast a portion of the tether is wrapped around a reel, the reelcomprising a commandable motor to rotate the reel, and a brake tocontrollably release the tether from the reel.
 24. A cargo airshipcomprising: a payload bay; a retractable payload door on an uppersurface of the cargo airship; a lifting gas reservoir; a releasablemass; and a commandable valve to control transfer of gas from thelifting gas reservoir to a high-altitude airship.